Chemical-contaminant mixtures are widely reported in large stream reaches in urban/agriculture-developed watersheds, but mixture compositions and aggregate biological effects are less well understood in corresponding smaller headwaters, which comprise most of stream length, riparian connectivity, and spatial biodiversity. During 2014–2017, the U.S. Geological Survey (USGS) measured 389 unique organic analytes (pharmaceutical, pesticide, organic wastewater indicators) in 305 headwater streams within four contiguous United States (US) regions. Potential aquatic biological effects were evaluated for estimated maximum and median exposure conditions using multiple lines of evidence, including occurrence/concentrations of designed-bioactive pesticides and pharmaceuticals and cumulative risk screening based on vertebrate-centric ToxCast™ exposure-response data and on invertebrate and nonvascular plant aquatic life benchmarks. Mixed-contaminant exposures were ubiquitous and varied, with 78% (304) of analytes detected at least once and cumulative maximum concentrations up to more than 156,000 ng/L. Designed bioactives represented 83% of detected analytes. Contaminant summary metrics correlated strong-positive (rho (ρ): 0.569–0.719) to multiple watershed-development metrics, only weak-positive to point-source discharges (ρ: 0.225–353), and moderate- to strong-negative with multiple instream invertebrate metrics (ρ: −0.373 to −0.652). Risk screening indicated common exposures with high probability of vertebrate-centric molecular effects and of acute toxicity to invertebrates, respectively. The results confirm exposures to broad and diverse contaminant mixtures and provide convincing multiple lines of evidence that chemical contaminants contribute substantially to adverse multi-stressor effects in headwater-stream communities.
|Title||Multi-region assessment of chemical mixture exposures and predicted cumulative effects in USA wadeable urban/agriculture-gradient streams|
|Authors||Paul Bradley, Celeste A. Journey, Kristin Romanok, Sara Breitmeyer, Daniel T. Button, Daren M. Carlisle, Bradley Huffman, Barbara Mahler, Lisa H. Nowell, Sharon L. Qi, Kelly Smalling, Ian R. Waite, Peter C. Van Metre|
|Publication Subtype||Journal Article|
|Series Title||Science of the Total Environment|
|Record Source||USGS Publications Warehouse|
|USGS Organization||California Water Science Center; Colorado Water Science Center; Maryland Water Science Center; New Jersey Water Science Center; Oregon Water Science Center; Texas Water Science Center; National Research Program - Central Branch; South Atlantic Water Science Center; Ohio-Kentucky-Indiana Water Science Center; WMA - Earth System Processes Division|